The study was small, with just 20 participants. And the effect was
modest, with the dark chocolate consumers showing an 11% increase in
maximal walking distance compared with no change in patients who ate
equal amounts of milk chocolate.

Loffredo and colleagues called the research a "proof-of-concept"
study, adding that bigger studies with longer follow-up times are needed
to confirm the findings.

Natalie Evans, MD, of the Cleveland Clinic, who was not involved with the study, said further research is warranted.